Turn-on Process Research Articles

Non-Dissipative Snubber Circuit Based SEPIC Converter for High Static Gain Applications

In this paper different non-dissipative snubber circuits in which RCD snubber circuit, CD snubber circuit, LCD snubber circuit and proposed LCD snubber circuit are implemented in SEPIC converter to obtain high static gain. The snubber circuit is used for the protection of the power semiconductor devices. The requirement of high static gain is necessary in different applications of dc-dc converters, so that efficient operation of the system can be obtained. The basic idea of the snubber circuit used in this paper is to reduce the turn-on and turn-off losses at the time of switching processes. For this purpose, inductor and capacitor combination is required so that during turn-on process, sudden change in current through semiconductor device which is used as a switch, can be reduced. Similarly, during turn-off process, sudden change in voltage across switch can be minimized. Here, different snubber circuit based SEPIC converters are analyzed with the help of MATLAB simulink and results of output voltages and currents are obtained. The results are summarized which clearly shows that the proposed SEPIC converter has high static gain in comparison of the others topologies. Hence non-dissipative snubber circuit based SEPIC converter provides high efficiency than the other modifications in SEPIC converter.

Gate Current and Snapback of 4H-SiC Thyristors on N+ Substrate for Power-Switching Applications

High-power switching applications, such as thyristor valves in a high-voltage direct current converter, can use 4H-SiC. The numerical simulation of the 4H-SiC devices requires specialized models and parameters. Here, we present a numerical simulation of the 4H-SiC thyristor on an N+ substrate gate current during the turn-on process. The base-emitter current of the PNP bipolar junction transistor (BJT) flow by adjusting the gate potential. This current eventually activated a regenerative action of the thyristor. The increase of the gate current from P+ anode to N+ gate also decreased the snapback voltage and forward voltage drop (Vf). When the doping concentration of the P-drift region increased, Vf decreased due to the reduced resistance of a low P-drift doping. An increase in the P buffer doping concentration increased Vf owing to enhanced recombination at the base of the NPN BJT. There is a tradeoff between the breakdown voltage and forward characteristics. The breakdown voltage is increased with a decrease in concentration, and an increase in drift layer thickness occurs due to the extended depletion region and reduced peak electric field.

Determination of Zinc Ion by a Quinoline-Based Fluorescence Chemosensor.

A novel fluorescence chemosensor XYQ for detecting Zn(II) was synthesized. XYQ showed fluorescence turn-on to Zn(II) with high sensitivity and selectivity in aqueous media among 19 metal ions. Its binding structure was demonstrated by ESI-MS, Job plot, and 1H NMR titration. The detection limit of XYQ to Zn(II) was 0.53μM. It is much below WHO drinking water standard (76.0μM). XYQ could be applied successfully to the test kit and real samples. The fluorescence turn-on process was possibly explained as a chelation-enhanced fluorescence (CHEF) effect with theoretical calculations.

Simplified analytical model for estimation of switching loss of cascode GaN HEMTs in totem-pole PFC converters

A practical analytical model to calculate the switching loss of cascode gallium nitride high electron mobility transistors (GaN HEMTs) is proposed. To facilitate analysis and application, the transmission delays introduced by Si MOSFET and interconnection inductances are ignored in modeling. Meanwhile, the nonlinear junction capacitances of the device and circuit stray inductances are also incorporated to increase the accuracy of the model. The turn-on and turn-off switching processes are described in detail and the simplified equations can be easily solved by using mathematical tools. Based on the analytical model, loss evaluation of totem-pole PFC converter is introduced briefly. Finally, the accuracy of the model is validated by comparing the calculated loss and converter's efficiency with experiment results. Peak efficiency of 99.26% is achieved for a 3.6 kW single phase CCM Totem-Pole PFC AC/DC converter switching at 50 kHz based on 650 V cascode GaN HEMTs.

Analysis and Experimental Evaluation of Middle-Point Inductance's Effect on Switching Transients for Multiple-Chip Power Module Package

Middle-point inductance ${{\boldsymbol L}_{{\boldsymbol {\text{middle}}}}}$ can be introduced in multiple-chip power module package designs. In this paper, the effect of middle-point inductance on switching transients is analyzed first using a frequency-domain analysis. Then a dedicated multiple-chip power module is fabricated with the capability of varying ${{\boldsymbol L}_{{\boldsymbol {\text{middle}}}}}$ , and extensive switching tests are conducted to evaluate the middle-point inductance's impact. Experiment result shows that the active mosfet 's turn-on loss decreases at higher values of ${{\boldsymbol L}_{{\boldsymbol {\text{middle}}}}}$ , while its turn-off loss increases. Detailed analysis of this loss variation is presented. In addition to the switching loss variation, it is also observed that different peak voltage stresses are imposed on the active switch and antiparallel diode during the switching transients. Specifically, in the case of lower mosfet 's turn-off, the maximum voltage of the lower mosfet increases as ${{\boldsymbol L}_{{\boldsymbol {\text{middle}}}}}$ goes up; however, the peak voltage of the antiparallel diode decreases significantly. The induced voltage spikes during upper mosfet turn-on process is also evaluated, and an opposite trend is observed experimentally. Analysis of the voltage overshoot variation is discussed. Based on the experimental evaluation and analysis, a multiple-chip power module package design guideline is summarized considering the middle-point inductance's effect.

An Intelligent Versatile Model-Based Trajectory-Optimized Active Gate Driver for Silicon Carbide Devices

Using silicon carbide (SiC) power devices can potentially improve the efficiency of a power electronic system, but it may also introduce severe electromagnetic interference (EMI) problems due to the fast switching speed. The conventional gate driver cannot provide the flexibility to adjust the switching speed of SiC dynamically. To address this issue, an intelligent versatile active gate driver (AGD) is proposed to achieve optimized switching trajectory for power devices. The proposed AGD has five operation modes, i.e., faster/normal/slower the turn-on process and slower/normal turn-off process. The availability of multiple operation modes offers extra freedom to improve the switching performance and enable it to be versatile across various systems. The proposed AGD can provide more switching speed adjustment resolution than the other AGDs allowing for fine tuning of the switching speed of SiC power devices. In addition, a novel modelbased trajectory optimization strategy is proposed to determine the optimal gate driver output voltage by trading the EMI noise against the switching energy losses. The functionalities of the multi-level AGD are validated with the experimental results. The hardware design consideration is also given for the product commercialization purpose.

Modified inductive power transfer topology for electrical vehicle battery charging using auxiliary network to achieve zero‐voltage switching for full load variations

Wireless inductive chargers are benedictional over plug-in chargers when human safety and convenience are the main concern. The advancement in the inductive chargers is yet less appreciable due to the loss of soft switching, low efficiency with load variation, and compatibility. In this study, a modified inductive power transfer capable DC–DC converter topology for electric vehicle battery charging is proposed. A simple auxiliary network is proposed and is supplemented with a modified pulse width modulation gating technique for achieving soft-switching over full load variations. In addition to achieving zero-voltage switching during turn-on and turn-off process, the proposed auxiliary network aids in the converter size reduction as compared with fourth order compensation topologies. This proposed topology also provides flexibility in switch selection, reduced switch stress. The operating principle and working of the proposed topology are validated through MATLAB simulations. Finally, experimental results obtained using a laboratory prototype rated for 600 W at 85 kHz are presented. The simulation and experimental results are found to be in good agreement with full load efficiency of 91.5%.

Mechanism analysis of IGBT turn-on process

Based on the internal structure of IGBT, the characteristics of gate voltage, collector current and collector-emitter voltage of IGBT during its turn-on process are studied in this paper. The relationship between gate voltage and gate capacitance is given, and the rising process of gate voltage is described in detail. According to the characteristics of IGBT turn-on current, a quadratic function is proposed to fit the collector current waveform. The influence of the main circuit stray inductance on collector-emitter voltage waveform is also analyzed. Finally, the IGBT dynamic switch characteristic test platform is built, and the measurement results verify the correctness of the analysis.

Endo- and Exo-Functionalized Tetraphenylethylene M12L24 Nanospheres: Fluorescence Emission inside a Confined Space.

The intrinsic relationship between the properties of green fluorescent protein (GFP) and its encapsulated small molecular light machine has spurred many biomimicking studies, aiming at revealing the detailed mechanism and further promoting its wide applications in different disciplines. However, how to build a similar confined microenvironment to mimic the cavity of a β-barrel and the fluorescence turn-on process is a fundamental challenge for both chemists and biologists. Herein, two distinct exo- and endo-functionalized tetraphenylethylene (TPE)-based M12L24 nanospheres with precise distribution of anchored TPE moieties and unique photophysical properties were constructed by means of a coordination-driven self-assembly strategy. Under dilute conditions, the nanospheres fluoresce more strongly than the corresponding TPE subcomponents. Meanwhile, the endo-functionalized sphere is able to induce a higher local concentration and more restrained motion of the enclosed 24 TPE units compared with exo-functionalized counterpart and thus induces much stronger emission due to the restriction of the rotation of the pendant TPE units. The biomimetic methodology developed here represents a promising way to understand and construct artificial GFP materials on the platforms of supramolecular coordination complexes.

A nano-molar fluorescent turn-on probe for copper(II) detection in living cells.

The development of fluorescent probes to detect trace metal ions in biological samples has been in great need. Herein, a fluorescence turn-on sensor (PHC) was designed for highly selective detection of Cu2+ ions. The probe PHC shows weak fluorescence due to imine isomerization. With Cu2+, a significant blue emission due to Cu2+-induced oxidation of imine to a carboxylate group is observed. The turn-on process is observed with a 63-fold increase of fluorescence quantum yield (from 0.004 to 0.252). The emission intensity has a good linear relation at Cu2+ concentrations of 0-40 μM. The detection limit is estimated as 8 nM (S/N = 3). The maximum emission change induced by Cu2+ is found in the pH range of 6.5-8.0. The probe PHC can be applied in detecting Cu2+ in living cells monitored by confocal fluorescence microscopy imaging.

Transient Temperature Field Analysis of Thyristor Turn-on Process under Narrow Pulse Width and Large Current

Thyristor will damage because of local overheating under narrow pulse width and large inrush current, if the selection is unreasonable. In this paper, the thermal field model of thyristor opening process is established and the transient temperature field distribution of thyristor is obtained by simulation. Simulation results show that under the narrow pulse width and large current, the temperature distribution on the silicon chip is not uniform, the temperature at the center gate is the highest, and the temperature is gradually decreased from the center point along the radius. The effect of current rise rate and chip radius on thyristor temperature distribution are simulated. Simulation results show that the higher the current rise rate, the higher the temperature of the thyristor center gate. The effect of chip radius on thyristor temperature is related to the pulse width of large inrush current. When the chip radius is smaller than the extended radius corresponding to the current pulse width, the smaller the radius, the higher the maximum temperature rise. When the radius of the chip is equal to or greater than the extended radius corresponding to the current pulse width, increasing the radius of the chip has no effect on the highest temperature rise.

Synthesis of a fractional-order PIλDμ-controller for a closed system of switched reluctance motor control

The relevance of creating high-quality control systems for electric drives with a switched reluctance motor (SRM) was substantiated. Using methods of mathematical modeling, transient characteristics of the process of turn-on of SRMs with various moments of inertia were obtained. Based on analysis of the obtained transient characteristics, features of the SRM turn-on process determined by dynamic change of parameters of the SRM during its turn-on were shown. Low accuracy of SRM identification using a fractionally rational function of rat34 class was shown. Regression coefficient of the resulting model was 85 %. Based on analysis of transient characteristics of the SRM turn-on process, a hypothesis was put forward about the possibility of identifying the SRM by means of a fractional-order transfer function. Using the methods of mathematical modeling, transient characteristics of the process of turning-on the SRMs with various moments of inertia were obtained. Using the FOMCON MATLAB Toolbox, identification of the SRM turn-on process with the help of a fractional-order transfer function of second order was performed. Regression coefficient of the resulting model was 93–96 %. For the obtained fractional-order transfer functions, a method of synthesis of a fractional-order PI λ D μ controller optimized in terms of minimum integral square error of the transition function of the closed system of fractional-order control of objects was implemented. The FOMCON MATLAB Toolbox was used for synthesis of the PI λ D μ controller. Comparative analysis of the SRM turn-on processes in both open and closed control systems with a classical integer-order PID controller and with a fractional-order PI λ D μ controller was made. Use of the fractional-order PI λ D μ controller in comparison with the classical integer-order regulator makes it possible to reduce overshoot from 13.3 % to 2.64 %, increase speed of the closed ACS, decrease regulation time from 1.48 s to 0.53 s while reducing variability of transient characteristics. The study results can be used to improve performance of closed systems for controlling angular velocity of the SRM

Impact of Termination Region on Switching Loss for SiC MOSFET

Due to outstanding properties of silicon carbide (SiC) and unipolar current conduction mechanism, the active chip size of SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) is significantly shrunk, which significantly improves switching performance. However, the termination region cannot be scaled down due to the existence of high breakdown electric field enclosing active region. Therefore, a SiC MOSFET switching loss model considering termination region effect is proposed in this paper with revealing physical insights into termination region during switching process. Furthermore, through theoretical analysis, model establishment, and simulation results, the loss breakdown under various blocking voltages (800, 1000, and 1200 V) for 1-, 3-, and 6-A current rated devices is obtained. ${E}_{\textsf {term}}$ and ${E}_{\textsf {acti}}$ as intrinsic loss of turn-on process make a significant contribution to the total switching loss under fast gate drive condition. The model shows that the turn-on and turn-off losses are under and overestimated, respectively, by using the commonly used electrical measurement. The loss from termination region aggravates the underestimation of turn-on loss and overestimation of turn-off loss further. The proposed loss estimation equation could provide accurate loss to help choose device and design power circuit for power electronic community. The results also raise new perspective to edge termination of efficient/reliable SiC MOSFET for device people.

Simulation design of high Baliga's figure of merit normally-off P[sbnd]GaN gate AlGaN/GaN heterostructure field effect transistors with junction field plates

In this paper, we conducted a numerical analysis on novel Normally-off PGaN gate AlGaN/GaN heterostructure field effect transistors with junction field plates (JFP-HFET). The breakdown voltage (BV) was significantly improved with the introduction of the junction field plate (JFP), which can make a rectangular distribution of the electric field in the GaN channel between the gate and the drain. The highest BV of 1340 V of JFP-HFET could be achieved with the gate to the drain distance Lgd = 6 μm, the length of the P-type region of the JFP Lp = 5.8 μm, the thickness of the JFP Tj = 500 nm, the doping concentration of P-type region of the JFP Np = 1 × 1017 cm−3, and the Al fraction of the AlGaN JFP xAl = 0.25. The optimum parameters of the JFP-HFET were achieved by considering both the principle of charge balance and the practical fabrication of the III-V devices. The highest Baliga's figure of merit (BFOM) 1.2 GW/cm2 was obtained under the conditions of Lgd = 6 μm, Lp = 5.8 μm, Tj = 100 nm, Np = 6 × 1017 cm−3, and xAl = 0.3. CV, turn-on and turn-off processes revealed that the JFP-HFET showed better switching characteristics than that of the HFET with metal field plate.

Voltage slope‐based zero voltage switching detection method for wireless power transfer systems

A zero voltage switching (ZVS) detection method, which relies on the half-bridge output voltage slopes during the MOSFET turn-on and turn-off transient processes, is proposed for the wireless power transfer (WPT) systems in this Letter. A voltage slope detection circuit and its active control method are also proposed to convert the nanosecond transient signal to a steady voltage level, which can be handled by the microcontroller easily. By having the information of the turn-on and turn-off voltage slopes, the state of ZVS can be evaluated to optimise the switching losses. A 500 kHz, three-coil resonant WPT system is built in order to evaluate the performance of the proposed detection method. Experimental results show that the ZVS state can be detected effectively. Also, the turn-off current can be controlled to a constant value to optimise the switching losses under the load and parameter variations.

A 1-kW CLTCL Resonant DC-DC Converter With Restricted Switching Loss and Broadened Voltage Range

A CLTCL resonant dc-dc converter is proposed in this paper. Through the dual-transformer architecture, the resonant characteristic of the converter alters and contributes to a wide input voltage range and a greatly broadened output voltage range from zero to the nominal. The transformer leakage inductors also participate in the resonating process, which eliminates their side effects on the conversion performance. Moreover, a simple and effective design method for converters with multiple resonant components is used to guide the resonant parameter design with the assistance of the MATLAB program. Soft switching for both turn-on and turn-off processes of all the inverter and rectifier switches is acquired, and the proposed converter, therefore, achieves lower switching losses among a wide load scope. In the end, a 1-kW prototype with a peak efficiency of 97.3% is fabricated in the laboratory to verify the working principle and design effect of the CLTCL converter.

A colorimetric and ratiometric dual-site fluorescent probe with 2,4-dinitrobenzenesulfonyl and aldehyde groups for imaging of aminothiols in living cells and zebrafish

Aminothiol levels are indicative of cellular and physiological statuses. A colorimetric and ratiometric dual-site fluorescent probe, NL-S, has been designed and synthesized. NL-S contains both a 2,4-dinitrobenzenesulfonyl group and an aldehyde group as recognition units for aminothiols. NL-S exhibited highly selective and sensitive detection of aminothiols, with a 27–44-fold enhancement of the fluorescent signal observed within 30 min of the addition of up to 20 equiv. of cysteine (Cys), homocysteine (Hcy) or glutathione (GSH) in aqueous media. The probe undergoes a turn-on excited-state intramolecular proton transfer process derived from cleavage and condensation reactions. The limits of detection for Cys, Hcy and GSH were 0.114, 0.146 and 0.202 μM, respectively. NL-S with negligible cytotoxicity was successfully employed to fluorescent imaging of aminothiols in living cells and zebrafish, suggesting good potential of NL-S in biological applications.

A Temperature-Dependent SiC MOSFET Modeling Method Based on MATLAB/Simulink

In this paper, a modeling method based on MATLAB/Simulink for a temperature-dependent SiC MOSFET in the entire working region was proposed. Using a supplementary test circuit, the output characteristics of a device in the saturated region were extracted. Based on these characteristics, the model covered the output characteristics of the device in the whole working region. From the output curves, three main parameters essential for modeling were derived. Based on the Si lateral double-diffused MOSFET model, a temperature-dependent static model of SCT20N120 was established by adding a temperature-dependent compensation voltage source to simulate the temperature characteristics of the threshold voltage and a temperature-dependent compensation current source to compensate for the drain current error in the linear region due to the differences in structure and material between Si and SiC. In addition, based on the gate equivalent circuit, the dynamic model of the target device was established. The temperature-dependent static simulation results could simulate the actual measured values well. Furthermore, based on the comparison between the dynamic simulation results involving the device’s turn-ON and turn-OFF process losses and the actual transient state losses derived from a double-pulse test under the conditions of $V_{\mathrm{ ds}}=300$ V, $I_{d}=15$ A, $R_{g\_{}exton}=18\,\,\Omega $ , and $R_{g\_{}extoff}=12\,\,\Omega $ at 200 °C, the maximum error was 6.7%.

Field-induced peculiarities in the dynamics of the director reorientation in confined nematic liquid crystals

The peculiarities in the dynamics of the director reorientation in confined nematic liquid crystals (LCs) under the influence of a strong electric field E directed at an angle α to the magnetic field B have been investigated theoretically on the basis of the hydrodynamic theory including the director motion with appropriate boundary and initial conditions. Analysis of the numerical results for the turn-on process, when the strong electric field E is suddenly applied, provides an evidence for the appearance of the spatially periodic patterns in confined LC film. Calculations show that when the angle α tends to be 90°, the optimum wavelength, giving the fastest response, provides the lower effective viscosity γeffα, which is less than one in the bulk nematic phase. So, a lower value of γeffα gives a faster relaxation times, as observed experimentally by using the time-resolved deuterium NMR spectroscopy.

Wideband modeling and transient analysis of sub-module in modular multilevel converter

PurposeThis paper aims to establish the wideband model of a sub-module in a modular multilevel converter (MMC) and analyze the switch transients of the sub-module.Design/methodology/approachThe paper builds an MMC sub-module test circuit and conducts dynamic tests both with and without the bypass thyristor. Then, it builds the wideband model of the MMC sub-module and extracts the model parameters. Finally, based on the wideband model, it simulates the switch transients and analyzes the oscillation mechanism.FindingsThe dynamic testing shows the bypass thyristor will add oscillations during switch transients, especially during the turn-on process. The thyristor acts like a small capacitor and reduces the total capacitor in the turn-on circuit loop, thus causing under-damped oscillations.Originality/valueThis paper found that the bypass thyristor will influence the MMC sub-module switch transients under certain circumstances. This paper proposes a partial inductance extraction procedure for the MMC sub-module and builds a wideband model of the sub-module. The wideband model is used to analyze and explain the switch transients, and can be further used for insulated gate bipolar transistor switch oscillation inhibition and sub-module design optimization.